How to Calculate Percentages: Simple Methods and Everyday Examples

Percentages appear in discounts, exam marks, taxes, interest, salary changes and nutrition labels. The word simply means "out of 100", and once you know four basic patterns you can solve almost any everyday percentage problem.

1. Find a percentage of a number

Result = number × percent ÷ 100

To find 15 percent of 240, calculate 240 × 15 ÷ 100 = 36. A mental shortcut is to find 10 percent by moving the decimal point one place (24), then add half of that for 5 percent (12), giving 36.

2. Find what percent one number is of another

Percent = part ÷ whole × 100

If you scored 45 marks out of 60, then 45 ÷ 60 × 100 = 75 percent. Always divide by the whole, the number you are comparing against.

3. Percent increase and decrease

Change % = (new value − old value) ÷ old value × 100

If a price rises from 80 to 100, the change is (100 − 80) ÷ 80 × 100 = 25 percent increase. If it later falls from 100 back to 80, the change is (80 − 100) ÷ 100 × 100 = 20 percent decrease. Notice that a 25 percent rise and a 20 percent fall cancel out, not 25 and 25. The base number is different each time, which is the most common source of confusion.

4. Add or subtract a percentage

• Discount: a 20 percent discount on 1,500 means paying 80 percent: 1,500 × 0.80 = 1,200.
• Add tax or a tip: to add 18 percent, multiply by 1.18.
• Raise or cut a salary: a 10 percent raise means multiplying by 1.10.

Working backwards from a final price

If a price including 18 percent tax is 1,180, the original price is 1,180 ÷ 1.18 = 1,000. A common mistake is to subtract 18 percent from 1,180. That gives 967.60, which is wrong because the 18 percent was calculated on the smaller original number, not on the total.

Percentage points are not percent

If an interest rate rises from 8 percent to 10 percent, it has gone up by 2 percentage points, but it has increased by 25 percent in relative terms (2 ÷ 8). News stories and ads often mix these up, so check which one is meant.

Successive percentages

Two discounts of 20 percent then 10 percent are not a 30 percent discount. Apply them one after the other: multiply by 0.80, then by 0.90, which equals 0.72. The total discount is 28 percent. The same logic applies to repeated growth, such as savings that earn interest each year.

Common mistakes to avoid

• Dividing by the wrong number. For percent change, divide by the old value.
• Adding percentages that apply to different bases.
• Forgetting to convert a percent to a decimal: 15 percent is 0.15.
• Rounding too early. Round only the final answer.

Let the calculator check your work

For quick checks, use our Percentage Calculator. It covers percent of a number, percent change and adding or subtracting a percentage. For loans, where percentages compound over time, see our guide to calculating EMI.

Frequently asked questions